The Deepwater Horizon oil rig burns more than 50 miles southeast of Louisiana's tip.

From staff and wire reports

NEW ORLEANS  Eleven crewmembers aboard an oil rig that exploded off the coast of Louisiana remained missing Wednesday afternoon as a team of U.S. Coast Guard cutters and rescue planes scoured the seas for survivors.

Deepwater Horizon, a large deep-water drilling vessel, exploded at around 10 p.m. Tuesday, critically injuring seven of its crewmembers, Coast Guard spokeswoman Elizabeth Bordelon said. Of the 126 crewmembers, 115 have been accounted for, she said.

The Coast Guard said 17 were taken by air or sea to hospitals. Four were reported in critical condition with severe burns. Others suffered burns, broken legs and smoke inhalation.

West Jefferson Hospital in suburban New Orleans said it treated four people, three of whom had been released. The University of South Alabama Medical Center said it was treating one person in its burn unit and evaluating five others.

Nearly 24 hours after the explosion, the rig continued to burn, and authorities could not say when the flames might die out. A column of boiling black smoke rose hundreds of feet over the Gulf of Mexico as fireboats shot streams of water at the blaze.

The rig is located around 52 miles south of Venice, La., in water around 5,000 feet deep, Bordelon said.

As the first dispatch for help came in, the Coast Guard scrambled four helicopters, five cutters and one fixed-wing plane to help in the search and rescues, she said. Five privately owned water vessels are fighting the fire aboard the Deepwater Horizon, which continues to burn, she said.

The cause of the explosion is still under investigation.

The rig was tilting as much as 10 degrees after the blast, but earlier fears that it might topple over appeared unfounded. Coast Guard environmental teams were on standby, though officials said the damage to the environment appeared minimal so far.

At the time of the explosion the rig was drilling but was not in production, said Greg Panagos, spokesman for its owner, Transocean in Houston. The rig was under contract to BP PLC. BP spokesman Darren Beaudo said all BP personnel were safe but he didn't know how many BP workers had been on the rig.

Panagos said it's still too early to know what caused the explosion.

"Our focus right now is on taking care of the people," he said.

Transocean vice president Adrian Rose saids crews were performing routine work before the explosion and there were no signs of trouble.

According to Transocean's website, the Deepwater Horizon is 396 feet long and 256 feet wide. The semi-submersible rig was built in 2001 by Hyundai Heavy Industries Shipyard in South Korea. The site is known as the Macondo prospect, in 5,000 feet of water.

The rig is designed to operate in water up to 8,000 feet deep and has a maximum drill depth of about 5.5 miles. It can accommodate a crew of up to 130.

A semi-submersible rig is floated to a drilling site. It has pontoons and a column that submerge when flooded with seawater. The rig doesn't touch the sea floor, but sits low in the water, where it is moored by several large anchors.

Last September, the Deepwater Horizon set a world deepwater record when it drilled down just over 35,000 feet at another BP site in the Gulf of Mexico, Panagos said.

"It's one of the more advanced rigs out there," he said.

Panagos did not know how much the rig cost to build, but said a similar rig today would run $600 million to $700 million.

Workers typically spend two weeks on the rig at a time, followed by two weeks off. It is equipped with covered lifeboats with supplies to allow them to survive for extended periods if they must evacuate.

Joe Hurt, a regional vice president for the International Association of Drilling Contractors, said working on offshore oil rigs is a dangerous job but has become safer in recent years thanks to enhanced training, improved safety systems and better maintenance.

"In recent years, there's been a lot more money available and more money spent on training and safety," he said.

Transocean has 14 rigs working in the Gulf of Mexico and 140 worldwide. There are 42 rigs either drilling or doing workovers — upgrades and maintenance — in depths of 1,000 feet or greater in the Gulf, according to the federal Minerals Management Service.

Since 2001, there have been 69 offshore deaths, 1,349 injuries and 858 fires and explosions in the Gulf of Mexico, according to the agency, which did not break down the cause of the deaths, the severity of the injuries, or the size of the fires and explosions.

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